1. Field of the Invention
The present invention relates to an NC machine tool which has a spindle for rotating a tool held thereby and is adapted to numerically control a relative movement between the spindle and a workpiece and to conduct a diagnosis on the run-out of the spindle.
2. Description of the Prior Art
The run-out of a spindle of a machine tool directly affects machining accuracies associated with the position, inner diameter and roundness of a machined hole. Therefore, the machine tool is inspected for the run-out of the spindle and conditioned so that the run-out of the spindle falls within a predetermined standard tolerance before delivery thereof from a machine tool maker to a user.
A typical method for the pre-delivery inspection is such that a cylindrical test tool having an outer circumferential surface finished with a high level of accuracy or a test tool having a spherical ball fixed to a shaft thereof is fitted in a taper hole of the spindle and rotated about an axis thereof, and the amount of a deflection of the outer circumferential surface of the test tool is measured, on the basis of which the run-out of the test tool is determined. Another known method for the inspection is such that a small-diameter parabolic mirror is attached to the center of a spindle nose, and a light beam from a microscope disposed with its optical axis substantially aligned with the center axis of the spindle is reflected on the parabolic mirror and projected onto a film through the microscope for imaging, and the run-out of the center axis of the spindle is determined on the basis of the result of the imaging.
A device for the pre-delivery inspection is provided separately from the NC machine tool. Where the run-out of the spindle is measured on a user side, the user has to provide such an inspection device on the user side.
As the NC machine tool is used for machining, the run-out of the spindle is gradually aggravated from an initial level observed at the delivery due to the aging of a bearing which supports the spindle. Therefore, it is preferred to regularly inspect the spindle for the run-out for prevention of a machining failure and a malfunction of the machine tool. With a recent tendency toward the speed-up of the machining, the rotation speed of the spindle has been increased to several hundreds thousand rpm (minxe2x88x921). Therefore, it is preferred to determine a static run-out observed when the spindle is rotated at a lower rotation speed as well as a dynamic run-out observed when the spindle is rotated at a higher rotation speed.
However, great costs are generally required for production of the inspection device on the user side, so that it is very difficult to prepare a special-purpose inspection device as described above on the user side.
A typical method for the determination of the run-out of the spindle on the user side is such that a test tool as described above is fixed to the spindle, and the run-out of the test tool is measured with the use of an indicator such as a dial gage while the spindle is slowly rotated with a probe of the indicator pressed against the outer circumferential surface of the test tool.
However, the indicator such as the dial gage has a measuring accuracy of about 2 xcexcm to 10 xcexcm, and is undoubtedly unsatisfactory as a run-out detector. Even if the regular inspection is conducted with the use of the indicator, there is virtually no change in the detected run-out. Therefore, the user refrains from the troublesome inspection operation, and tends to neglect to conduct the regular inspection. In most cases, the user inspects the spindle for the run-out after occurrence of a machining failure to find the cause of the machining failure.
In view of the foregoing, it is an object of the present invention to provide an NC machine tool which allows for a check for the run-out of a spindle thereof at any time.
In accordance with the present invention to solve the aforesaid problems, there is provided an NC machine tool which has a spindle for rotating a tool held thereby and is adapted to numerically control a relative movement between the spindle and a workpiece, the NC machine tool comprising: deflection detecting means provided on a base within a machining area for detecting a deflection of an outer circumferential surface of a test tool attached to the spindle when the test tool is rotated about an axis thereof; and run-out diagnosing means for conducting a diagnosis on the run-out of the spindle by calculating the amount of the run-out of the spindle on the basis of the deflection detected by the deflection detecting means and comparing the calculated run-out amount with a predetermined tolerance.
In accordance with the present invention, the test tool attached to the spindle is manually or automatically moved so that the outer circumferential surface thereof is located within a detection area of the deflection detecting means. Then, the test tool is rotated about the axis thereof, and the deflection of the outer circumferential surface thereof is detected by the deflection detecting means provided on the base within the machining area. Subsequently, the run-out diagnosing means calculates the amount of the run-out of the spindle on the basis of the detected deflection, and compares the calculated run-out amount with the predetermined tolerance for the diagnosis on the run-out of the spindle.
In the present invention, the diagnosis on the run-out of the spindle can be achieved through a very simple and easy operation by moving the test tool attached to the spindle so that the outer circumferential surface thereof is located within the detection area of the deflection detecting means. Therefore, a user of the NC machine tool can easily perform a regular run-out diagnosing operation in a daily work at any time. By thus performing the regular run-out diagnosing operation, a machining failure and a malfunction of the machine tool can be prevented.
The deflection detecting means comprises a main body having an insertion hole for receiving the test tool, and a non-contact type deflection detecting sensor fixed to the main body with a detecting portion thereof projecting in the insertion hole. The main body is fixed to the base, and the deflection of the test tool is detected by the non-contact type deflection detecting sensor with the test tool inserted in the insertion hole of the main body.
Since the deflection of the test tool is detected with the test tool inserted in the insertion hole of the main body, the test tool can exactly and properly be positioned with respect to the deflection detecting sensor simply by inserting the test tool into the insertion hole. Therefore, the positioning of the test tool can easily be achieved by manually moving the test tool. Further, the deflection of the test tool can be detected with a high level of accuracy by exactly positioning the test tool.
The deflection detecting means may include at least two non-contact type deflection detecting sensors disposed with deflection detecting directions thereof being perpendicular to each other.
The spindle runs out of its rotation center axis not only evenly but also eccentrically in one direction. In such a case, if a single deflection detecting sensor for the detection of the deflection of the test tool is located in a position where the deflection is smaller, the deflection of the test tool (i.e., the run-out of the spindle) cannot accurately be detected. With the aforesaid arrangement, the at least two deflection detecting sensors are disposed with the detecting directions thereof being perpendicular to each other, so that even the eccentric run-out of the spindle can assuredly be detected by either one of the deflection detecting sensors. Thus, the run-out of the spindle can accurately be detected.
The deflection detecting means may include two pairs of non-contact type deflection detecting sensors disposed in diametrically opposite relation with deflection detecting directions of one pair of non-contact type deflection detecting sensors being perpendicular to deflection detecting directions of the other pair of non-contact type deflection detecting sensors.
With this arrangement, the two pairs of non-contact type deflection detecting sensors disposed in diametrically opposite relation with the deflection detecting directions of the one pair being perpendicular to the deflection detecting directions of the other pair, so that the run-out of the spindle can more accurately be detected.
The run-out diagnosing means may be adapted to conduct a diagnosis on a static run-out observed when the spindle is rotated at a lower rotation speed and on a dynamic run-out observed when the spindle is rotated at a higher rotation speed.
As described above, the spindle is rotated at several hundreds thousand rpm (minxe2x88x921) for the speed-up of the machining. Therefore, it is preferred to determine the static run-out of the spindle rotated at the lower rotation speed as well as the dynamic run-out of the spindle rotated at the higher rotation speed. With the aforesaid arrangement, the diagnosis is conducted on the static run-out of the spindle rotated at the lower rotation speed and on the dynamic run-out of the spindle rotated at the higher rotation speed, so that the spindle run-out diagnosing operation can be performed in a suitable manner for the higher-speed machining. The term xe2x80x9clower rotation speedxe2x80x9d herein means a rotation speed up to 100 minxe2x88x921 and, for stable measurement of the deflection, the lower rotation speed is preferably not higher than 100 xe2x88x921. The term xe2x80x9chigher rotation speedxe2x80x9d herein means a rotation speed higher than the lower rotation speed. The higher rotation speed is preferably the highest possible rotation speed, as long as data can properly be sampled by a controller. More preferably, the higher rotation speed is a rotation speed closer to a natural frequency of the spindle to provide stricter measuring conditions.